The present-day stringent emission standards for motor vehicles dictate a closer look to feedgas emission reduction. Major sources of hydrocarbon (HC) emission with respect to the conventional combustion chamber construction are cold start, fuel inhomogeneities, crevice volumes inside the combustion chamber, wall wetting, and quality of combustion.
The contribution of cold start to HC emissions stems from the difficulty of fuel evaporation and the forming of a combustible mixture. The normal wall wetting and puddling of the liquid fuel in the intake port and on the intake valve, and even on the piston top make it difficult to develop a robust control strategy for cranking and startup of the engine.
In the construction to be described, sonic air flow through a valve is used to aid fuel evaporation and air/fuel mixing. The effect of crevice volume loading with unburned hydrocarbons is essentially eliminated by keeping the fuel away from the crevices. And, finally, the combustion quality is enhanced by controlling the fluid dynamics inside the combustion chamber by means of piston motion and proper combustion chamber design.
It is well understood that the motion of the fluid at the time of spark ignition plays a dominant role in providing good engine combustion. Normally this flow motion is generated in the intake process which requires a careful design of the intake runner, intake port, and intake valve and cylinder head interface. Nevertheless, a large percentage of the intake generated flow may decay by the time of ignition.
To generate a required flow field at the time of ignition, the combustion chamber in this case is moved from its conventional location, either in the piston top or between the cylinder head and piston, to a cavity inside the cylinder head, as indicated in the drawings. The combustion chamber and main cylinder displacement/swept volume chamber now communicate through an appropriately designed small connecting channel with a valve at the exit of the chamber and entrance to the channel. Using the piston motion and the smallness of the connecting channel, an intense flow field inside the combustion chamber can be generated at the time of spark ignition to not only vaporize the fuel, but provide excellent mixing of the air and fuel to assure combustion wholly within the combustion chamber. To accomplish this, the spark plug and fuel injector both would be located in the combustion chamber wall.